In the field of rapidly developing display technology, the LED as display device plays a more important role, and the driving and control technologies of the LED also become more important. The driving modes for the LED are roughly divided into two types, of which one is to drive by a constant voltage, and the other is to drive by a constant current. The luminance of the LED increases as the current passing therethrough increases, and the internal resistance of the LED have a slight variation during illuminating and heating. Thus, driving the LED by the constant current is better and more stable than by the constant voltage.
Under a condition of driving by the constant current, the currently common control modes for the luminance of the LED are of two types. One is to connect multiple LEDs in series, and the control for LED luminance is to load a certain control technology in the driving circuit. In such case, it is only to control the whole series of the LEDs, and there is no way for changes in the luminance of one or several LEDs among the whole series of LEDs without affecting the luminance of other LEDs. The other control mode is that a driving circuit to drive only one or several LEDs and to load the luminance control technology in the driving circuit. This luminance control solution is costly and low effective, and it may be applied for displaying in a case of small number of LEDs and without considering cost. However, in a large scale of illumination, such as backlight lamps for a liquid crystal display, this approach is not applicable due to too many LEDs.